Hydraulic cycling system



W. T. STEPHENS HYDRAULIC CYCLING SYSTEM4 Naw.l 16, 19.48.

2 SheevtsfSheet l med my 2z,` 1944 :z5 Om WILLIik/L TSTEPHENS Nov. 16, 1948. w. T. STEPHENS HYDRAULIC CYCLING SYSTEI 2 Shawmut 2 Filed l# 22, 1944 Patented Nov. 16, 1948 HYDRAULIC CYCLING SYSTEM William T. Stephens, Cleveland, Ohio, assignor to Hydraulic Control Engineering Company,

Cleveland, Ohio, a corporation of Ohio Application MayZZ, 1944, Serial No. 536,781

This invention relates to hydraulic systems, and more particularly to systems for providing for and controlling automatic sequential or cycling operations of hydraulic presses, punches and other fluid actuated reciprocating machinery and tools.

Itis the general object ci the present invention to provide a novel and improved hydraulic system, of the type described.' making use of a plurality of automatically charged, differential pressure accumulators and hydraulically actuated cycling means for applying the pressures from these accumulators in predetermined time sequences to the reciprocating mechanism. A A An important object of the invention consists in the operation of a double acting hydraulic cylinder in predetermined andadJustable time cycles by means of pressures built up in high and low pressure accumulators, one intended to provide sufficient pressure for the power stroke and the other for the release or return stroke, the timing of the cycles as well as the rate of movement and length of both the 4advancing and retracting strokes being wholly hydraulically controlled. y

Animportant feature of the invention resides in the connection between the return side of the hydraulic cylinder and the low pressure accumulator which permits the constant re-use of the same fluid and the automatic cyclic charging of this accumulator from the pressure available in the high pressure accumulator.

Another important feature of the invention resides in the means for controlling the power actuated valve between the power side of the reciprocating mechanism and the high pressure accumulator under the regulation of a manual hydraulic valve whereby the speed of thecyling can be accordingly regulated.`

Still another important feature of the invention comprises the use of compressed air on one side of each of the accumulator pistons together with the use of air pressure regulating valves and air relief valves so arranged that each accumulator at all times maintains an almost exact fluid Claims. (Cl. 60-51) be made in the several parts of the system as fall within the scope of the appended claims without departing from the spirit of the invention. In said drawing; Fig. l is a wholly diagrammatic and schematic showing of a hydraulicrsystem arranged in accordance with the present linvention, pipes and ducts being illustrated by single lines with arrows designating the directions of fluid now.

vices as presses, punches, grinding and lapping pressure whereby phase-positioning in the operat- I emplary embodiment of the inventiornit being understood that such changes and variations may machines, breaches and the like, considerable diiiiculty has heretofore been experienced in the cyclic control, in regulating thefstroke length and the phasing of the same. except by the `use of complicated, cumbersome, expensive and Iobstructing mechanisms on the hydraulic power cylinder itself. Such devices have taken the form of links, cams. lugs, reciprocating rods and levers i with their appurtenant adjusting devices for actuating valves or relays for stopping and starting the flow of pressure uid to one or the other end of the plunger.

In accordance with the present invention no mechanism whatsoever is mechanically associated with or mounted on or adjacent the power cylinder. The cycling, phasing and stroke length is entirely controlled hydraulically and from points as far removed from the power cylinder as desired. y

ForV a betterl understanding of the invention reference should be had to the accompanying drawing where at ills represented broadly any form of hydraulically actuated reciprocable machine. comprising a, hydraulic cylinder I2 having therein a piston I4 of the double acting type provided with a piston rod I5 extending through the lower head i8 and associated with the reciprocal portion I1 of the machine. Pressure fluid for lifting cr retracting the piston Il and its assoelated part I1 isV introduced near the lower end of the cylinder through port 20 while high pressure iluid for performing the power stroke'is introduced through the upper head ported as at 2 I'.

To 4provide the requisite pressure iiuids for actuating the piston a pair of' accumulators are connected respectively to the ports 20 and 2l, the low pressure or retracting accumulator being indicated. at 22 while the high pressure or working stroke accumulator is depicted at 24. These accumulators in general are of similar construction each including a conventional cylinder fitted with a reciprocable piston 26 guided by a piston rod 21 shown as attached to the lower ace thereof and extending through the lower cylinder head 3J.

Pressure for application to the liquid, which is received in the space beneath the piston and compressed against the lower cylinder head, is provid'- ed by compressed air or gas taken from the line 3| appropriately supplied by any conventional compressing apparatus to a sufllcient pressure to provide the desired fluid pressures on the upper sides of the pistons, when considering the differential areas on the two heads of the accumulator pistons as provided by appropriately sizing the piston rods,

In order that the fluid pressure from each accumulator may be maintained at substantially a constant value under all working conditions and at all parts oi' the accumulator and power piston strokes, the space above the piston in each accumulator is connected to the air line 3| through a suitable pressure regulating valve 33, which is adjustable to provide the desired fixed outlet pressure for delivery to the respective accumulators.

On the return stroke of each accumulator piston after having delivered Vliquid from the lower side thereof the full cylinder of compressed air must have its pressure relieved in order to maintain the entering fluid beneath the accumulator piston at its desired pressure, and this is achieved by having connected through the upper head of each accumulator a pressure relief valve 85 which may be constructed in the nature of a safety valve and adjustable to provide blow-oil at the proper pressure to maintain the fluid pressure beneath the piston at the desired optimum amount.

The low pressure or retracting accumulator 22 is refilled with fluid after each of its discharge strokes from the power cylinder by the superior pressure existing in the power accumulator 24, but some other means must be provided for refilling the fluid side of the high pressure accumulator when its fluid has been discharged, and this takes the form of any suitable high pressure liquid pump such as that illustrated at d0. This may be the simple gear pump which should be constructed to provide pressures of more than 1000 pounds p. s. i. It is arranged to be driven, for instance,

by a direct connected electric motor 4l supplied from mains i2 under the control of a switch 03. This switch is actuated from one to the other of its two posit-ions by means of a pair of lugs 56 and 5 spaced apart on a rod-like extension t6 of the main piston rod 21 of accumulator 2li. When the accumulator is fully charged with liquid, as shown in the drawing, the lug t eri-- gages the switch arm opposite its fulcrum and opens the circuit to the motor. When the accumulator is substantially discharged the lug M engages the switch arm, closes the circuit and starts the motor and pump to refill the main accumulator. f

A reservoir, sump or tank 50 for hydraulic fluid is connected by pipel 5i to the inlet side of the pump 40 to always maintain it supplied with fluid. The pump discharges into outlet pipe 52 which has a connection back to the tank through an adjustable pressure relief valve 53 set to provide protection for the pump and motor in the event of stoppage in any of the liquid lines. The pump outlet pipe 52 is connected by pipe El to the lower end of the accumulator 24 through check valve 55 which prevents any return flow from the accumulator to the pump particularly when thelatter is n ot in operation.

For initially charging the smaller accumulator.

fluid is available from the pump through pipe 56 and manual valve 58 which is normally closed after the accumulator 22 has been -filled with fluid. To prevent damage to the smaller accumulator and its 4associated equipment, pipe 5E is vented back to tank by way of line 59 and pressure relief valve 60.

In order that the power cylinder may be manipulated manually for the purpose of setting dies, determining the desired length and phase of stroke, or the like, fluid can be delivered to the same from accumulator 24 by way of pipe 82, manually controlled valve 63 having control lever 64, pipe 65 from the outlet of said valve, to pipe 66 leading into the portv 2i ofthe cylinder. The valve 63 is part of a dual valve structure with both Valves supplied with high pressure fluid from the accumulator through a manifold connected to a pipe 62. The valves are likewise arranged to vent fluid baci:l to the tank through a manifold connected to pipe 68.

The valve 63 is a three-position valve having a closed or neutral intermediate position which prevents the flow of fluid to or from the ram via pipe 65. In another of its positions it permits high pressure fluid to be delivered from pipe 62 into pipe 65 and hence to the ram for lowering the same. In the third position of valve 63 the high pressure manifold, connected to pipe 62, is completely closed off and the fluid above the piston of the ram is allowed to pass` back through pipes 66, 65 and the valve to be returned through pipe 68 in the tank 50. This permits raising of the piston I4 by the action of the low pressure fluid coming from the accumulator 22 and pressing against the underside of piston I4.

Automatic cyclic operation of the power cylinder is achieved through the use of a spring-loaded valve 10 connected between pipe 66 and pipe 62 and by-passing the manual valve 63. This valve l0 has a roller on its operating plunger springpressed against and actuated by a cam 'l2 driven at any regulated speed by'means of` a hydraulic motor I3 receiving its operating liquid through pipe line 62 from the high pressure accumulator and discharging the used liquid through pipe 'M into discharge line 59 returning to the tank.

The valve l0 provides for the control of the liquid-for actuating the press ram so that high Vpressure liquid is delivered to it in one position of the valve and in the only other position this liquid is connected for delivery to the reservoir and the flow of high pressure liquid is shut ofi. This eliminates any lower position dwell from the press platen I1 but if such is desired it can be provided in an obvious manner. The high pressure liquid flowing to valve 'IIJ from pipe 62 connected to accumulator 24 moves via manual valve 16, associated with valve 63 in the manner previously described, and delivers fluid to pipe 'I1 branched to include pipe 78 supplying actuating fluid for the motor 13, and pipe 19 leading to valve '10.

Both pipes 18 and 19 are provided with manually adjustable needle valves Bil and 3| respectively. Needle valve 80 provides for .minute adjustment of the speed of the liquid motor 73 which determines the time length of each cycle of operation oi the power piston. Valve 8i determines the quantity of fluid delivered to the power stroke of the piston and when manipulated jointly with valve 60 permits a minute regulation of the distance length of the power stroke which can readily be determined experimentally or mathematically.

Thus knowing the length of-dwellof the .cam lobe for opening the valve 10 and knowing the rate ot ilow of the valve for each of its settings it will be simple to determine thequantity of fluid available for displacement of the power piston at -any speed of the motor 10.

the use of a valve 05 in the pipe 50 between the i low pressure accumulator and the port 20 on the underside of the power piston. This valve permits full and unrestricted iiow from the power cylinder back to the accumulator and hence offers no restriction'on the power stroke which can thus be timed exactly by manipulation of4 the needle valves Just described. On the return stroke. however, when the fluid from the upper,Y side of the piston is returning freely to the tank via pipe 05, valve 10, oil line 81, manual valve and oil line 00, some means must be provided to control the rate of flow of low pressure retracting nuid to the underside of the power piston and this is achieved by having valve 85 manually adjustable to restrict the iiow in that direction only. Such a valve may take the form of that disclosed in the application of William C. Dolch, Serial No. 481,893, for Flow controlling valve, filed April 5, 1943, now Patent 2,367,106, dated January 9, 1945.

Valve 1,6, which has the operating handle 89,

has only two operating positions, the nrst one providing for complete shut-off of flow oi both high pressure and return fluids in any direction through the valve and is used"for stopping the oil motor and the delivery of high pressure oill to the -power cylinder so that automatic operation is terminated. When moved into the other position the valve 89 permits ilow from pipe 52 into pipe 11 thus delivering oil both to the motor and to` valve 10 which'controls its delivery tol the power piston. In this Esame position the valve provides for a flow of return fluid from the power piston via pipe 81 into line 68 conducting it to tank 50. This control ofthe return iluid by valve 15 insures its cut-oil.' when the valve' is properly manipulated so that irrespective of the position in which the motor stops no movement of the power piston will continue. This insures full manual control by means of valve 53 when setting the press.

For convenience in construction and simplification of the piping, the control valves 53 and 16 have been combined into a single unit, as clearly illustrated in Fig. 2, wherein the one-piece housing |00 contains a pair of longitudinal valve bores |02 and |04 parallel to each other and arranged to accommodate respectively the valve plungers |06 and |08 having longitudinal reciprocation therein under control of handles 64 and BEI.4

A common high pressure inlet port ||0 is arranged for connection to the pipe 62 from the high pressure accumulator and a common low* pressure discharge port is arranged for connectionto the low pressure vdischarge line 68. The upper valve plunger controls flow to and from a port I I 2` adapted to be connected to line 65. The valve is shown with the plunger in the neutral position, which permits flow from passage l0' to transfer passage ||4 around the necked portion- ||5 of the plunger |06. This provides for high pressure nuid delivery to valve plunger |00.

6 l When, however,- plunger |00 is positioned either to the lett or the right `ot the position shown, chamber ||0 and passage ||4 is closed oil by the'i'ull diameter portions of the plunger, cutting out the operation oi' the lower plunger. When it is desired to deliver high pressure nuid tooutlet port ||2 the handle 04 is moved to the right until radial bores IIB register with ||0' vdelivering iiuid into chamber ||1 inside of the valve plunger which lifts check valve H0 from its seat and delivers iiuid through the radial ypassages lisinto ||2. Any return action is prevented by the check valve. When it is desired to return iluid from the press by way of pipe 05 and port ||2 the plunger |00 is moved to the left until radial passages ||0 cooperate withu||2, whereby nuid is delivered 4through the check ward the left from the position shown being prevented by engagement of the leftend withy the solid .block |22 closing the end of the bore. In the position shown all `ports and passages are closed so that liquid cannot be delivered to line 11, which is attached to port |24; nor can return y fluid from valve 10 via line 81 escape fromfrport |25. This insures immobilizing the press plunger in spite of the stopping position of valve 10'. v

' When the press is to be put into operation valve handle 89 is moved to the right, in, which position it will stay when the hand is removed. When so positioned radial ports |25 register Vwith transfer passage |I4 so that high pressure fluid flows into -the interior of chamber |21, pushing open check valve |28 and flowing out through passages |29, now registering with |24. `This position of the valve disconnects ||4 from the groved area |30 of the valve plunger, which latter now registers with port |25 so that fluid returning from valve 10 enters radial passages |3|, ows into chamber |32 within the valve, pushes open check valve |33 and discharges through radial passages |34, now registering with chamber |35 connected by passage |36 to discharge port Y As an illustrative example of the operation of the power press, it will be assumed that the high pressure accumulator is capable of supplying fluidy at a constant pressure of 1000 p. s. i. and that this -pressure is sufiicient, when applied to 'the top of piston- |4 of the ram, to move the to raise the platen when the 1000 p. s. i. pressure is relieved from the top of the piston.

As shown sin the drawing the ram is fully raised and held in this position by the action of the' low pressure accumulator shown practically exhausted but still exerting its full pressure on the uid below its piston and that on the lower side of the ram. Valves 58,'63 and 16 are closed.

y, The several valves 63, 10 and 15 do not provide a by-pass from high to low pressure when -in any position. The high pressure accumulator will fue fully, charged as will be Stopped. With the system at rest the operator has only to move valve 16 by-manipu lation of its lever 89 to permit flow of fluid from the high pressure accumulator to the oil motor and to valve 10 which provides for the cyclic operation of the ram as previously mentioned. It will be noticed that when the ram plunger is being forced downwardly the pressure from the low pressure accumulator acts continuously on its lower face so that the available working pressure is substantially the difference betweenthe pressures in the two accumulators except for the slight variation caused by the presence of the piston rod l which provides differential areas on the two sides of piston I4.

Accumulator 22 is recharged by the mere downward movement of piston i4 on the power stroke. Each accumulator is maintained at the desired oil pressure by the combined action of the pressure regulating valves and the pressure relief valves 33 and 35 respectively, operating on the air side of the accumulator.

Not only is fluid expended from accumulator 24 for the operation of the ram, since this fluid is returned to the tank and not to the accumulator, but some is also used for driving the motor 13. The pump is therefore required to replenish this accumulator from the supply of oil in-tank 50. If the capacity of the accumulator 24 is not muchgreater than that of the ram at full stroke. the accumulator will be charged about once per stroke of the ram. y

- To assure proper operation at all times the following rules should be observed:

1. The uid capacity of accumulator 22 should exceed the amount required to raise the ram piston from its lower to its .upper position at maximum stroke.

2. The pressure in accumulator 22 should not be substantially greater than that necessary to withdraw the platen I1.

3. The volume delivered from the pump 40 per unit of time should exceed the maximum volumetric requirements of the operated units during the same time period.

By observing rule i the piston 26 of the low pressure accumulator can be prevented from ever yreaching its maximum top or bottom positions and thus the pressure of the fluid in this accumulator can vary only as the air pressure above the piston varies. This is maintained substantially constant by valves 33 and 35. Proper setting of the'limit stops 44 and 45 for controlling the pump switch will prevent the piston of accumulator 24 from ever reaching its top and' bottom positions. The fluid pressure in this ac 7 illustrated and the pumpv cumulator will remain constant for'the reasons 1 pointed out in connection withaccumulator 22.

Proper phasing as well as stroke length of the hydraulic ram is' achieved as previously mentioned by adjustment of needle valves 80 and 8l and the flow regulating valve 85. Further changes in the cycling may be effected by subl stituting cams of other shapes and dwells for that shown at 12 thus making possible a wide variety of applications and uses fora unit of the type described for producing reciprocating motion entirely by hydraulic means.

One distinguishing feature of the system is the use of the low pressure accumulator to provide constant pressure on the return side of the ram insuring instantaneous return of the work unit upon release of the pressure used on the power stroke. This arrangement also makes possible a -only to block or allow flow of high pressure fluid.

There is no reversal of now of the high pressure fluid in this valve'as in the case of a conventional double acting valve and thus less heat is generated and the system runs much cooler. Furthermore, the -simple shutting or opening of the pipe line can be accomplished in a shorter period of time than that required to 'make a complete reversal of flow direction and hence this system lends itself to more rapid operation while acting with less shock due to the cushioning effects of the accumulators. By means of the needle valve 80 supplying oil to the motor an almost infinite range of speeds for the ram is possible. This,

together with the other variants already de.. scribed, makes possible almost a limitless number of operating characteristics to suit practically any need. After the proper combination has been selected control of the entire system for stopping and starting is obtained by manual operation of valve16.

I claim:

l. In a system of the type described, in combination, a double acting hydraulic cylinder and piston, a source of low pressure fluid continuously connected to the cylinder to urge said piston in onedirection, a source of high pressure fluid of substantially constant pressure having a connection to the opposite end of said cylinder, a-

valve in said last mentioned connection adapted to be positioned only to connect said source to said cylinder or to connect the cylinder to waste, mechanism for periodically moving said valve alternately to its two positions including a uid actuated continuously running rotary motor. means connecting said motor to said source of high pressure fluid and a cam driven by said motor to actuate said valve, a manual valve jointly controlling the flow of uid to said first valve and to the said motor, said last mentioned valve also controlling the discharge from the first valve and an independent valve for determining the xed speed of the motor to thereby regulate the length of stroke of the piston.

`; 2. In a system of the type described, in combination, a double acting hydraulic cylinder and said motor to one of said sources of pressure iiuid,

a throttling valve in said means to regulate the speed of the motor to thereby control the cycling rate of the piston, a manual valve for controlling the flow of uid to the said first valve, means in said manual valve to control the waste flow from said first valve and a second manual valve arranged to by-pass theperiodic valve and having advancing, retracting and holding positions whereby the power piston may be manipulated manually in spite of the position of stopping of the periodic valve.

3. In a system of the type described, in combination, a double acting hydraulic cylinder and piston, a source of low pressure fluid continuously connected to the cylinder to urge said piston in one direction, a source of high pressure fluid having a connection to the opposite y,end of said cylinder, ya valve in said last mentioned connection adapted to be positioned to connect said source to said cylinder or to connect the cylinder to waste, mechanism for periodically moving said valve alternately to its two positions including a fluid actuated motor, means connecting said motor to one of said sources of pressure fluid, a throttling valve in said means to regulate the speed of the motor to thereby control the cycling rate of the piston and a throttling valve in each of the pressure fluid connections to the cylinder to regulate the length of stroke of the piston.

4. In a system of the type described, in combination, a double acting hydraulic cylinder and piston, a source of low pressure fluid continuously connected to the cylinder to urge said piston in one direction, a source of high pressure huid having a connecton to the opposite end of said'cylinder. a valve in'said last mentioned connection adapted to be positioned to connect said source. to said cylinder or to connect the cylinder to waste, mechanism for periodically moving said valve alternately to its two positions including a fluid actuated motor, means connecting said motor to one of said sources of pres sure fluid, a throttling valve in said means to regulate the speed of the motor to thereby control the cycling rate of the piston and a throttling valve in each of the pressure fluid connections to the cylinder, the said valve inthe low pressure accumulator to hydraulic cylinder connection being constructed to restrict flow to the cylinder but not away from it. l

5. A system for the automatic cycling control oi a hydraulic press having a double acting piston ,in a cylinder, comprising, a low pressure hy-t draulic accumulator continuouslyconnected to the return side of the press cylinder to retract the piston, a high pressure hydraulic accumulator aving a connection to the opposite side of the press cylinder to actuate the piston on the power stroke against the pressure in the first accumulator, a valve in said high pressure connection constructed to connect the press cylinder either to the high pressure accumulator or to a sump, mechanism for alternately positioning said valve in one or the other of its two positions and including interchangeable rotary cams of varying dwells to actuate the valve in4 accordance with a predetermined cycle, power means for driving said mechanism, speed control means for said power means, a manually operable on and ofi.

valve interposed between the first mentioned valve and the high pressure accumulatorand constructed to simultaneously shut off both the high pressure flow and the return of liquid from the press to said sump, and a regulating valve between said rst and second mentioned valves to determine the rate of press operation independent of the speed of said power means.

6. A system for the automatic cycling control of a hydraulic press having a double acting pision in a cylinder, comprising, a low pressure hydraulic accumulator continuously connected to the return side of the press cylinder to retract the piston, a high pressure hydraulic accumuconnection between the press valve in one or the other of its two positions in accordance with a predetermined cycle including a cam and a rotaryhydraulic power means therefor, speed control means for said power means, a manually adjustable throttling valve in each and an accumulaitor. whereby. in conjunction with the speed control, the length of press stroke and position thereof can be accurately controlled, the throttling valve for the high pressure accumulator being positioned between it and said alternately positioned valve. Y

7. A system for the automatic cycling control ,of a hydraulic press having a double acting piston in a cylinder, comprising, a low pressure hydraulic accumulator continuously connected to the return side of the' press cylinder to retract the piston, a high pressure hydraulic accumulator having a connection to the opposite side of the press cylinder'to actuate the piston on the power stroke against the pressure in the first accumulator, a valve in said high pressure connection constructed to connect the press cylinder either to the high pressure accumulator or to a sump, mechanism for alternately positioning said valve in one or the other oi its two positions in accordance with a predetermined cycle, power means for driving said mechanismspeed control means for said power means, a manually operable on and oil valve interposed between the first mentioned valve and the high pressure accumulator and constructed to simultaneously shut off both the high pressure now and the return of liquid from the press to said sump, and a manually controlled valve by-passing the rst and second -mentioned valves to permit full manipulation of the press for initial set-ups etc.

8. A system for the automatic cycling control of a hydraulic press having a double acting piston in a cylinder, comprising, a low pressure hydraulic accumulator continuously connected to the return side of the press cylinder to retract the piston, a yhigh pressure hydraulic accumulator having a connection to the Opposite side oi the press cylinder to actuate the piston on the A accumulator, a valve in power stroke against the pressure in the first said high pressure connection-constructed to connect the press cylinder either to the high pressure accumulator or to a sump, mechanism lfor alternately positioning said valve in one or the other of its two positions in accordance with a `predetermined cycle, throttling means between said valve and accumulator, a rotary hydraulic motor connected to drive said mechanism, a liquid duct connecting vsaid motor and high pressure accumulator to provide fluid for driving the motor, a manually controlled throttling valve in said duct to regulate the speed of the motor and a manual valve positioned to simultaneously control the flow to said motor and to and from said first valve.

9; A system for the automatic cycling control of a hydraulic press having a double acting pislater having a connection to the opposite side ton in a cylinder, comprising, a low pressure hydraulic accumulator continuously connected to the return side of the press cylinder to retract the piston, a high pressure hydraulic accumulator having a connection to the opposite side of the press cylinder to actuate the piston on the power stroke against the pressure in the ilrst accumulator, a valve in said high pressure connection constructed to connect the press cylinder either to the high pressure accumulator or to a sump,

mechanism' for alternately positioning said valve -said cylinder, a

in one or the other of its two positions in acA cordance with a predetermined cycle, fluid actuated power means for driving said mechanism, speed control means for said power means, a manually adjustable throttling valve in each con nection between the press and an accumulator, whereby, in conjunction with the speed control, the length of press stroke and sition thereof can be accurately controlled, the throttlingvalve in the press to low pressure accumulator connection being constructed to open fully in the direction of flow of liquid from the press to the accumulator and a two position manual valve in the outlet from he high pressure accumulator arranged in oneiposition to connect said accumulator to the first valve` and to the power means and in the1 other position to shut ofi' now from the accumulator, said two position valve being arranged to pass the discharge valve to the sump in its first position and in its second position to prevent said discharge.

10. A system for the automatic cycling control of a'hydraulic press having a double acting piston in a cylinder, comprising, a low pressure hydraulic accumulator continuously connected to the return side of the press cylinder to retract the piston, an adjustable valve in said connection adapted to regulate only the rate of flow to high pressure hydraulic accumulator having a connection to the opposite side of the press cylinder to actuate the piston on the power stroke against the pressure in the rst ac cumulator, a valve in said high pressure connection constructed to connect the press cylinder either to the high pressure accumulator or to a sump, mechanism for alternately positioning said valve in one or the other oi' its two positions in accordance with a predetermined cycle, a hyirom the rst.

' draulic Amotor connected to nism, a liquid duct connecting drive said mechahigh pressure accumulator driving the motor, a`manually controlled throttling valve in said duct to regulate the speed of the motor, means to continuously maintain a substantially constant pressure charge in said high pressure accumulator. and a manually operable "on and oiT valve interposed between the high pressure accumulator and the nrst men tioned valve and constructed to simultaneously shut oil? both the ,high pressure flow' and the return of liquid from the press to said sump, said on and oil valve being so arranged in the system that it shuts oif the flow of high pressure liquid to said motorA simultaneously :with that to said first mentioned valve.

WILLIAM T. STEPHENS.

REFERENCES CITED UNITED STATES PATENTS Coates Apr. 10, 1945 said motor and to vprovide nuid for l 

